1. Field of the Invention
The present invention generally relates to an abnormality detection device and, more particularly, to an abnormality detection device for detecting an abnormality in a communication via a communication bus, and a microcomputer connected to the communication bus.
2. Description of the Related Art
Recently, semiconductor devices having various communication protocols have been developed. Also, a system has been developed in which system a plurality of semiconductor devices are connected to each other by a communication bus and, when any one of the semiconductor devices operates as a master, the other semiconductor devices are made to operate as slaves, i.e., subordinately, to the semiconductor device operating as a master. The communication bus in this system is called a “multi-master communication bus”.
Accordingly, a circuit for monitoring a communication status in such a system as mentioned above is becoming an important factor in securing a reliability of a communication in the system and a reliability of the system itself. In this circuit, timeout detection is conventionally employed as a monitoring method. With the “timeout detection”, when next information is not received within a predetermined time, an abnormal state such as a trouble is assumed to occur.
However, the conventional timeout detection only monitors a response time from other semiconductor devices and a state of congestion in a communication bus. Additionally, the conventional timeout detection is realized simply by software, only securing a minimal reliability of a communication.
Recently, however, such a system as mentioned above is becoming more and more complicated, and thus, an unexpected communication abnormality, a delay of a communication and the like occurring in the communication bus of the system may adversely influence the whole system. Therefore, a higher reliability of the communication is required to be secured.
Conventionally, to elevate the above-mentioned reliability, such a measure has been taken as making a program to raise a frequency of monitoring the communication bus and executing the program in a device having a CPU. However, this disadvantageously puts a heavy load on software including the program. Also, this is faced by another problem that a throughput of the system limits a frequency of monitoring the communication bus, deteriorating an accuracy of the timeout detection.